The thunderstorm that spawned a tornado there triggered more twisters in Georgia three hours later.

'This could be the worst tornado in Alabama's history,' said meteorologist Josh Nagelberg of AccuWeather.com.

Marshall County in northeastern Alabama had six fatalities, five of them in one house, Sheriff Scott Walls told Reuters.

'That house was in the direct path of the tornado. We had homes and businesses that took direct hits. Every community in the county has suffered damage,' he said.

President Barack Obama declared a state of emergency for Alabama and ordered federal aid for the stricken state.

'While we may not know the extent of the damage for days, we will continue to monitor these severe storms across the country and stand ready to continue to help the people of Alabama and all citizens affected by these storms,' Obama said in a statement on Wednesday night.

Floods and power outages

Floods were a big concern throughout the storm-hit area, where rain compounded with melted snow to cause rising rivers and saturated soils.

Several states suffered power outages as well as property and infrastructure damage that could prove costly to repair.

The storms forced the Tennessee Valley Authority to close three nuclear power plants in Alabama and knocked out 11 high voltage power lines.

Governors in Alabama, Arkansas and Tennessee declared a state of emergency and in Mississippi, Governor Haley Barbour declared a state of emergency for 39 counties.

Earlier, authorities put the death toll across the South at 25 over a three-day period, a figure that included 11 deaths in Arkansas, six in Alabama, five in Mississippi, two in Louisiana and one in Tennessee.

Two deaths were reported later Wednesday after a tornado hit Georgia near the border with Tennessee and Alabama.

Residents in Tennessee are coping with flooding, power outages and blocked roads. Flooding became more widespread in Arkansas on Wednesday after several days of intense storms.

Violent weather has pummeled much of the US South this month. Two weeks ago, at least 47 people died as storms tore a wide path from Oklahoma to North Carolina. – Reuters